A VFIS motor is a motor that may run at a rotational frequency that is independent of an amplitude, frequency, and phase of an alternating current (AC) power signal used to power the motor. Further, typical AC motors may achieve rotational frequencies that are independent of an amplitude, frequency, and phase of a driving AC power signal using rectifiers and inverters that perform full-power level power conversions of the driving AC power signal. VFIS motors, on the other hand, may operate without performing such full power rated power conversions.
Starting a VFIS motor by connecting it directly to an AC bus may cause damage to the stator windings of the VFIS motor. For example, because a non-moving VFIS motor does not create a significant electrical impedance within the stator windings, a sudden surge of power may cause a short circuit within the windings resulting in significant heat, and possible breakdown. Applying a sudden starting current to the VFIS motor may cause its electrical components to wear out prematurely.
Additionally, typical speed control techniques, such as variable frequency drive techniques and field-oriented control techniques may not work with VFIS motors because the VFIS motors may have active windings on both a stator and a rotor. As such, new starting techniques and new techniques for speed control are needed within the industry to accommodate VFIS motors. Other disadvantages may exist.